Mesoscale Analysis of a Local Extreme Precipitation Event in Wuhan Area during Poor Meiyu Season
武汉地区少梅年一次局地强降水中尺度系统 特征的分析

Since 2000, the main Meiyu front rainband moved northward to the Huaihe River basin. The poor or no Meiyu occurred in the Yangtze River very often, due to the anomaly of the atmospheric circulation. However, in poor Meiyu season, a heavy rainfall still occurred in Wuhan area during 0000 UTC 29 June-0000 UTC 30 June 2009. The mentioned above case is diagnosed by using NCEP data, operational observation from China Meteorological Administration, four times per day SCHeREX sounding, automatic weather stations data, radar data, FY-2C Black Body Temperature (TBB), and CMORPH data. It is noticed that the Baikal trough as cold air source favorable the heavy rainfall occurrence has been replaced by the ridge. However, the other favorable factors still benefit the precipitation. They have been noticed that: 1) Existance of col pressure field in East Asia provided the important condition for formation of mesoscale disturbance to the eastern part of the Tibetan Plateau. 2) Eastward shifting trough from the Tibetan Plateau intensified the vertical motion in the middle reaches of the Yangtze River and a meso low formed between Chongqing City and Hubei Province which was very helpful for heavy rainfall in Wuhan. 3) Westward extending of the West Pacific Subtropical High forced the low level jet to intensify in Jiangxi and Hunan provinces and Low Level Jet (LLJ) transported very rich moisture to the Wuhan area. 4) Overlaying of the cold and dry in upper troposphere on the warm and moist in low troposphere produced the significant potential instability. High Convective Available Potential Energy (CAPE) value was released and the convection was initiated due to the triggering of the mesoscale disturbance. 5) The small meso-b scale convective systems relating directly with the heavy rainfall in Wuhan have been revealed.